1. Field of the Invention
The present invention relates to an optical semiconductor device and a manufacturing method therefor. In particular, it relates to a technology of a deep ultraviolet light emitting device using a group III-V compound semiconductor.
2. Background Art
In recent years, in technical fields of semiconductor light emitting devices using PN junction, such as light emitting diodes and laser diodes, nitride semiconductors containing nitrogen as a group-V element have been drawing lots of attention, and research and development thereof have been actively carried out. Nitride semiconductors, such as AlN, GaN and InN, are direct transition semiconductors. Furthermore, a ternary or quaternary mixed crystal is capable of emitting light from infrared rays to deep ultraviolet rays by changing the band gap by appropriately determining the composition.
Furthermore, a semiconductor light emitting device that has a light emitting layer made of AlGaInN as a quaternary mixed crystal and emits ultraviolet rays is drawing attention (see the JP Patent Publication (Kokai) No. 9-64477A (1997)). It has been reported that, although the AlGaInN layer contains In, the AlGaInN layer can have a light emission peak at a wavelength of 360 nm or shorter, and the internal quantum efficiency thereof can be improved to approach that of the InGaN layer.